Various hybrid powertrain architectures are known for managing the input and output torques of various prime-movers in hybrid vehicles, most commonly internal combustion engines and electric machines. Series hybrid architectures are generally characterized by an internal combustion engine driving an electric generator which in turn provides electrical power to an electric drivetrain and to a battery pack. The internal combustion engine in a series hybrid is not directly mechanically coupled to the drivetrain. The electric generator may also operate in a motoring mode to provide a starting function to the internal combustion engine, and the electric drivetrain may recapture vehicle braking energy by operating in a generator mode to recharge the battery pack. Parallel hybrid architectures are generally characterized by an internal combustion engine and an electric motor which both have a direct mechanical coupling to the drivetrain. The drivetrain conventionally includes a shifting transmission to provide the preferable gear ratios for wide range operation.
One hybrid powertrain architecture comprises a two-mode, compound-split, electro-mechanical transmission which utilizes an input member for receiving power from a prime mover power source and an output member for delivering power from the transmission. First and second electrical machines are operatively connected to an energy storage device for interchanging electrical power between the storage device and the electrical machines. A control unit is provided for regulating the electrical power interchange between the energy storage device and the electrical machines. The control unit also regulates electrical power interchange between the electrical machines.
Engineers have a challenge in managing transitions in operating states of hybrid powertrain systems to minimize effect on vehicle driveability caused by driveline lash, or play, in the entire gear train. Actions wherein driveline torque is transitioned from a positive torque to a negative torque, or from a neutral torque to a positive or negative torque can result in gear lash, clunks, i.e. audible noise, and jerks, as slack is taken out of the driveline and driveline components impact one another. Excessive gear lash, clunks, jerks, and other related events may result in operator dissatisfaction, and can negatively affect powertrain and transmission reliability and durability.
Gear lash, clunks, and jerks have the potential to occur during vehicle operations including: when the operator changes transmission gears, e.g. from neutral/park to drive or reverse; when the operator tips into or out of the throttle; or when the vehicle is operated on an inclined surface. Lash action occurs, for example, as follows: Torque-generative devices of the powertrain exert a positive torque onto the transmission input gears to drive the vehicle through the driveline. During a subsequent deceleration, torque input to the powertrain and driveline decreases, and gears in the transmission and driveline separate. After passing through a zero-torque point, the gears reconnect to transfer torque, in the form of motor braking, electrical generation, and others. The reconnection of the gears to transfer torque result in gear impact, with resulting clunks and jerks.
Hybrid powertrain systems such as the exemplary two-mode, compound-split, electro-mechanical transmission have multiple torque-generative devices. Coordinated control of the torque-generative devices is required to reduce driveline gear lash, clunks, and jerks. Additionally, the exemplary hybrid powertrain system introduces a challenge of managing driveline transitions which may occur when one of the motor/generators transitions from operating in a motoring mode to operating in a generating mode.
Therefore, there is a need for a control scheme for hybrid powertrain systems such as the exemplary two-mode, compound-split, electro-mechanical transmission having multiple torque-generative devices which addresses the aforementioned issues related to driveline gear lash and clunks. This includes a scheme that is cognizant of driveline torque transitions which may occur when one of the torque-generative devices comprises an electrical machine which transitions between operating in a motoring mode and operating in a generating mode. There is a further need to develop a hybrid powertrain control system which can coordinate and manage power from the torque-generative devices in a manner which effectively uses on-board computing resources.